Separate bpf and struct util from netlink util library

1. Separate bpf and struct libraries from netlink library.
2. Rename bpfmap jni library to respect its java side library.
3. Add README to explain the rules of adding shared jni library.
4. Also allow packages/modules/Connectivity to use bpf library.

Bug: 205088391
Test: atest TetheringTests
      atest CtsTetheringTest
      atest TetheringPrivilegedTests
      atest ConnectivityCoverageTests
Change-Id: I6e668818bede63b241cd901c0967f401613ddaf6
diff --git a/staticlibs/tests/unit/Android.bp b/staticlibs/tests/unit/Android.bp
index a9f9d70..07a8200 100644
--- a/staticlibs/tests/unit/Android.bp
+++ b/staticlibs/tests/unit/Android.bp
@@ -17,6 +17,7 @@
         "androidx.test.rules",
         "mockito-target-extended-minus-junit4",
         "net-utils-device-common",
+        "net-utils-device-common-bpf",
         "net-tests-utils",
         "netd-client",
     ],